治疗床两侧金属C型臂对吸收剂量的影响

摘要

objective: To investigate the influence of metal C-arm on absorbed doses for Precise accelerator.Methods: Solid water phantom was placed in the centre of tennis racket panel and the distance from ion chamber to the panel were 5 cm and 10 cm respectively.The involved gantry angels were measured for different field sizes crossing the right C-arm which had 7 fixed positions.Transmission factors of the right-side C-arm were measured using 0.6 cm3 ion chamber for 6 MV and 15 MV X-ray with fixed gantry angle and rotational fields.Results: From 90°to 180°, the involved range of gantry angles was largest while the right C-arm was at R7.The restrict range of gantry angle enlarged with larger field size and smaller treatment depth.The dose deviation caused by C-arm increased with the beam energy and the distance through which the beam passed C-arm.For rotational beams, larger dose errors were found when the C-arm was closer to the linac isocenter.Conclusions:There is large deviation of absorbed dose caused by the C-arms of the treatment table.It is desirable to avoid the C-arm inside field in treatment planning and patient setup.%目的:研究加速器治疗床两侧金属C型臂对吸收剂量的影响.方法:测量模体置于治疗床板中央,电离室插孔到床板距离分别为5 cm和10 cm.右侧C型臂分别置于7个不同角度,确定不同面积射野经过C型臂时的机架角度.利用0.6 cc电离室测量6 MV和15 MV X线经过C型臂后固定野照射吸收剂量的变化,以及C型臂位置对旋转照射吸收剂量的影响.结果:机架角为90°～180°,治疗床右侧C型臂位于R7位置时,机架角度布野受限范围最大;机架角布野受限范围随射野面积的增大而增大,随治疗深度的减小而增大.对固定野照射,射线能量越小,吸收剂量的衰减越大;射线穿过C型臂的距离越大,吸收剂量的衰减越大;旋转照射时C型臂位置越靠近床板中心轴,吸收剂量衰减越大.结论:治疗床两侧金属C型臂对射线有衰减和散射,造成吸收剂量及其分布发生变化.治疗计划设计和患者摆位时应尽量避开金属C型臂.